Establishing jet scaling patterns with a photon

Abstract

Staircase and Poisson scaling are two typical patterns we observe for the exclusive number of jets at high energy hadron colliders. We examine these scaling properties for photon plus jets production at the LHC and find that this channel is well suited to study these features. We illustrate and discuss when to expect each of the two patterns, how to induce a transition through kinematic cuts, and how photons are related to heavy gauge bosons. Measurements of photon+jets production is therefore providing valuable information on exclusive jet scaling, which is going to help to eventually understand the theoretical origin of exclusive jet scaling properties in more detail.

Scaling patterns for QCD jets

“…First, the classical Z+jets channel should JHEP10(2012)162 be used to study the transition from Poisson to staircase scaling using a simple kinematic cut on the leading jet. A similar proposal exists for γ+jets production [13]. In addition, QCD gap jets already probe these scaling features through the measured average number of gap jets.…”

“…In figure 2 we show jet ratios R (n+1)/n for a large range of n. Indeed, we observe Poisson as well as staircase scaling. The same behavior is known from hadron colliders for example in pp → γ+jets production [13]: for relatively low n values the emission is dominated by large scale differences, inducing a Poisson pattern. For large jet multiplicity individual emissions are not affected by a large scale difference, so we see a staircase tail.…”

“…Using the parton shower picture as well as generating functionals we have found that a Poisson distribution is tied to a large hierarchy of scales and a logarithmically enhanced radiation matrix element. Such different scales can be induced by kinematic cuts, for example in Z+jets [1] or γ+jets [13] production. Many effects, like non-abelian gluon splittings, phase space limitations, or sub-leading logarithms modify the pure Poisson shape of the exclusive n jets distribution.…”

“…Understanding the jet multiplicity and the jet spectra from QCD radiation is a core ingredient to improving any of these analyses. Even though jet radiation seems to follow simple patterns [10][11][12][13], theoretical predictions for multi-jet observables in perturbative QCD are challenging. It is clear that the radiation of relatively hard quarks and gluons is a direct consequence of the hierarchy between the large proton-proton collider energy and the typical electroweak scale of the…”

Parton-shower uncertainties with Herwig 7: benchmarks at leading order

“…This also applies to validating new approaches against existing data, as well as using predictions to design future observables and/or collider experiments. Phenomenological studies, for example, indicate that MC event generators can be used even in primarily data driven methods to perform powerful analyses once theoretical uncertainties are under control [50,51]. It is therefore important to quantify the uncertainties associated with an event generator in a reliable way.…”